The present application claims priority upon Japanese Patent Application No. 2003-355202 filed on Oct. 15, 2003 under 35 USC 119(a), which is herein incorporated by reference.
The present invention relates to an intermediate transfer system provided in an image forming apparatus using an intermediate transfer technique and a method for cleaning an intermediate transfer belt that is a component member of the intermediate transfer system. In particular, the present invention relates to an improvement to stabilize the cleaning of the intermediate transfer belt.
Conventionally, a color image forming apparatus using an electrophotographic technique such as a color copier or a color printer is provided with a plurality of developing devices, where visible images (toner images) having a different color from developing device to developing device are formed, and eventually these toner images are superimposed and transferred on one and the same recording sheet.
A technique using an intermediate transfer belt (in general, referred to as “intermediate transfer technique”) is known as one embodiment of the color image forming apparatus of this type. In the intermediate transfer technique, a developing apparatus for each color is provided, and an optical image obtained by splitting an image into different color components is formed on a photosensitive drum as an electrostatic latent image for each color. Then, the electrostatic latent image is developed to provide a toner image for each color. Then, the respective toner images are superimposed on the same area of an intermediate transfer belt for first transfer, so that a synthesized image of full color is obtained on the intermediate transfer belt, and then the synthesized image is transferred on a recording sheet at one time for the second transfer. Furthermore, when forming monochrome images, a black toner image is first transferred on the intermediate transfer belt using only the developing device corresponding to black images, and the black toner image is secondly transferred on a recording sheet. For example, JP2000-338744A, JP2001-324905A, JP2002-14542A, and JP2002-304104A are known to disclose the image forming apparatus of this type.
A conventional intermediate transfer system provided in an image forming apparatus using such an intermediate transfer technique will be described below.
In a conventional intermediate transfer system as shown in FIG. 9, an intermediate transfer belt c is suspended over a driving roller a and a driven roller b, and a tension roller d for applying a constant tension to the intermediate transfer belt c is pressed onto the inner face of the intermediate transfer belt c. This tension roller d is provided movably, and the tension of the intermediate transfer belt c can be kept constant by the movement thereof even if the state in which the belt is suspended over each roller is changed. Furthermore, this intermediate transfer system is provided with a cleaning blade e for collecting residual toner that is left on the surface of the intermediate transfer belt c after the second transfer onto a recording sheet, and an opposing roller f is provided on the inner face of the intermediate transfer belt c that is opposed to the cleaning blade e. In other words, the intermediate transfer belt c is sandwiched between the cleaning blade e and the opposing roller f, and a frictional force is applied between the outer surface of the intermediate transfer belt c and the cleaning blade e so that the residual toner can be collected. Furthermore, a screw g for conveying toner is provided in the vicinity of the cleaning blade e, and the residual toner collected by the cleaning blade e is conveyed and discharged by the screw g.
Photoreceptors h, h, . . . are provided for respective colors, opposed to the outer surface of the intermediate transfer belt c, and rollers for the first transfer i, i, . . . are provided on the inter face of the intermediate transfer belt c, opposed to the corresponding photoreceptors h, h, . . . . Each roller for the first transfer i is movable in the direction in which the roller for the first transfer i can be in contact with or apart from the photoreceptor h. In a standby time, as shown in FIG. 9A, the roller for the first transfer i have receded from the photoreceptors h. Thus, the outer face of the intermediate transfer belt c is away from the photoreceptors h, h, . . . When forming color images, as shown in FIG. 9B, each of the rollers for the first transfer i, i, advances toward the photoreceptor h, h, . . . Thus, the outer face of the intermediate transfer belt c is brought in contact with each of the photoreceptors h, h, . . . so as to be ready for the first transfer. At the time of forming monochrome images, only the roller for the first transfer i of the developing device that corresponds to black images advances toward the photoreceptor (photoreceptor for black images) h, and thus the outer face of the intermediate transfer belt c is brought in contact with the photoreceptor h for black images so as to be ready for that first transfer (transfer of monochrome images). Furthermore, the suspension state of the intermediate transfer belt c is changed with such movement of the rollers for the first transfer i, i, . . . , so that the belt tension is changed. However, the tension roller d is moved (in the horizontal direction) in FIG. 9, so that a constant tension is applied to the intermediate transfer belt c.
In the structure as described above in which the tension roller d is moved to provide a constant tension to the intermediate transfer belt c, the inclination angle of the span of the intermediate transfer belt c between the tension roller d and the cleaning blade e is varied with the position to which the tension roller d is moved (in the state of FIG. 9A, the inclination angle is large, and in the state of FIG. 9B, the inclination angle is small. As a result, the angle at which the surface of the intermediate transfer belt c is in contact with the cleaning blade e is changed, or the force with which the cleaning blade e is pressed onto the surface of the intermediate transfer belt c is changed, and therefore stable cleaning performance may not be obtained. Consequently, residual toner is left continuously on the surface of the intermediate transfer belt c and this residual toner may be attached to the recording sheet so that the image quality may be affected adversely, or the residual toner may drop from the intermediate transfer belt c to soil the internal portion of the apparatus.
The present invention is carried out in view of these aspects, and the object thereof is to provide an intermediate transfer system that can avoid the state in which residual toner is left continuously on the surface of an intermediate transfer belt by cleaning the intermediate transfer belt stably and a method for cleaning an intermediate transfer belt.